Electrode for mercury devices



Oct. 25, 1938. s. s. GREEN ELECTRODE FOR MERCURY DEVICES FiledApril 8, 1957 Patented Oct. 25, 1938 UNITED STATES PATENT OFFICE Duncan Electric Manufacturing Company,

'La Fayette, Ind., a corporation of Illinois Application April 8, 1937, Serial No. 135,708

20 Claims.

This application relates to electrodes for completing an electric circuit through mercury. Although the invention has been illustrated as embodied in a combined switch and circuit breaker,

5 it is of general utility wherever a metallic member is to make contact with mercury and it has particular value whenever the circumstances are such that it is not easy to completely and dependably seal the device to exclude air therefrom.

In all devices in which mercury forms part of an electrical circuit it is, of course, desirable that the resistance the electrodes and their contact resistance with the mercury be very low. This is especially true in the case of mercury circuit 15 breakers which take the place oi. ordinary fuses and would be detrimentally affected by the heat which would be generated if the contact resistance were substantial. The requirement for low resistance immediately eliminates a great 20 many materials from possible use as electrodes. The materials which are less obviously excluded (except platinum, which is very expensive) all seem to be subject to oneor both of two defects. Some of them, such as gold, silver, copper, alu- 25 minum, tin and zinc, are dissolved by the mercury or otherwise adversely aflected by it and others, such as iron, nickel, and stainless steels, will oxidize in the presence of air especially at high temperatures and are unsatisfactory once they 39 have oxidized because the oxide coating is an effective insulator.

Of course, when it is practical to completely seal the device .and excude all air, iron may be used as an electrode as in the simple type of mer- 35 cury switch now common which is sealed within a small glass tube. In mercury devices such as circuit breakers which cannot be readily dependably sealed in commercial practice there has been a very difficult problem of providing a satisfac- 40 tory electrode. Accordingly, an object of the present invention is to solve this problem by providing an electrode which in practice will not oxidize even at the high operating temperatures encountered and which will not be too greatly 45 afiected by the mercury.

A further object is to provide such electrodes which will not harmfully contaminate the mercury. It should be explained in this connection that gold and silver, although rapidly dissolved 50 by mercury, are harmless in it unless present in excessive proportions; while a copper electrode, which is not rapidly dissolved, will so contaminate the mercury that the mercury will not flow properly through the fine bore of the circuit breaker 55 and may even leave a thin conductive film therein,

(Cl. zoo-152) Applicant has discovered that it is necessary either for the electrode to be non-oxidizing and not soluble in mercury or for it to includea metal which amalgamates with mercury so as to protect the electrode from being insulated by oxidation, though the electrode must nevertheless neither contaminate the mercury excessively nor be exces'sively affected by it. Except by the .very costly use of platinum, these requirements have seemed, before applicant's invention, to be irreconcilable. Applicant, however, has reconciled them by providing in an electrode the combinauon of a small amount of contact metal and a structural metal which preferably has no reaction with the mercury and serves to limit any adverse effects between the contact metal and the mercury. Various specific combinations which are satisfactory are set forth hereinafter.

Additional objects and advantages will be apparent from the following description and from the drawing, in which:

Fig. 1 is a view of the combined mercury circuit breaker and switch chosen for illustration of the invention, the cover being removed for the sake of clarity.

Fig. 2 is a detail view of a form of the feed electrode of the device of Fig. 1, having a spot of special electrode material applied thereto.

Fig. 3 is a side elevation of the same.

Figs. 4 and 5 are corresponding views of the discharge electrode; and

Fig. 6 is a fragmentary sectional and exploded view of a modified form of electrode.

Although this invention may find many uses, only one has' been chosen for the purpose of 11- lustration, this one use presenting special problems which make the invention necessary and especially advantageous. This illustrated use is in connection with a combined mercury circuit breaker and switch which may generally be un-' 40 derstood from Fig. 1 and which is more fully described in applicant's Patent No. 2,003,260, issued May 28, 1935. A control tube ii is carried within a housing i2 which is formed of two telescoping halves rotatably mounted on any suitable support, not shown,- and is formed of two telescoping halves one of which has been removed in Fig. 1. The control tube ll communicates with the feed tube i3 through which mercury is fedinto. the control tube Ii, the mercury normally assuming the position shown in Fig. 1. One electrode it, called the feed electrode, ex-

tends into the mercury in the feed tube II. An-

other electrode II, called the discharge electrode, extends into the mercury which lies in a well l8 communicating with the bore l9 or the control tube l l. Current passing between electrodes l6 and i! will flow through the mummy and due to the resistance of the mercury in the restrictedbore M! will heat the mercury in this bore. When the current flow is beyond the value for which the circuit controller is rated, it will heat the mercury in the control bore #9 to such extent that this mercury will vaporize and any unvaporized mercury will be expelled by the vaporized mercury, thus breaking the circuit just as a fuse would break the circuit by melting. In the case of extremely heavy overloads, the mercury may be vaporized with explosive suddenness. Furtherafter the mercury has been discharged due to an overload as above described and circuit controller may be restored to its normal condition simply by'inverting it so that the point 2i of the housing I? is positioned at the bottom so that the mercury flows to that point, after which the entire unit is rotated in a clockwise direction so that the funnel shaped portion 22 of the housing will act as a scoop to pick the mercury up and drain it into the feed tube it from which it flows into the control tube ii, any excess overflowing to form a reserve pool of mercury 23. The unit may also be used as a switch to break the circuitmanually (as in turning off the current for repairs) simply by inverting the unit so that all of the mercury runs to the point 2!, thus flowing out of the passage between the electrodes l6 and ill.

From the foregoing description it may be understood that the electrodes in such circuit breakers have special requirements. As has already been mentioned, they must be able to withstand arcing. This ability can not be otherwise defined if very short or very heavy, their resistance can be correspondingly higher. They must have extremely low contact resistance with the mercury not only because any resistance represents power loss but also because heating of the mercury due to contact resistance might seriously interfere with the proper functioning of the circuit controller. v

In connection with having low .contact resistance it is important that they should not oxidize in practice even at the fairly high temperatures at which the circuit controller may operate, since oxidation of the electrodes would greatly increase their contact resistance, the oxide forming an insulating layer around the electrode. In circuit controllers of the illustrated type it is not desirable to have to seal the housing so tightly that air and oxygen can be excluded from within the housing and in fact it might be impossible to exclude the air dependably. As a result, iron and nickel (which would otherwise be good electrode materials) are not satisfactory. Their contact resistance may be low initially but sometimes gets much too high due to oxidation.

Another requirement of the electrodes is that aisaeee they should satisfactorily withstand the effect of continued contact with hot mercury. This tends to eliminate the metals which are not eliminated by oxidation. For example, copper, even if ox= idation is prevented, is rendered brittle by long exposure to the mercury and, furthermore, dissolves somewhat in the mercury. If enough copper is exposed to the mercury, the mercury becomes so contaminated that it will not flow properly through the constricted control bore it and may even leave a conductive film thereon. Aluminum also contaminates the mercury and fur-= thermore oxidizes and is unable to withstand the effect of arcing. Gold and silver are not only too expensive but are completely dissolved away in mercury. Although they happen to be harmless to the mercury, it is obviously vital that the electrodes shall not be dissolved away. Although platinum would be satisfactory, it is obvious that it is much too expensive to be used except in minute quantities.

The two common metals which are able to satisfactorily withstand the efiect of mercury are iron and nickel but, as previously mentioned, both of these oxidize too readily when heated and, as

a result, neither of them have low contact resistance except under ideal conditions and hence they are not dependable. In other words, it so happens that all of the cheap metals are unsatisfactory either because they are unable to withstand the eifect of mercury or because their contact resistance is bad at least when they are exposed to air so that they oxidize. On account of this difliculty of oxidation the various metals which have been used as electrodes in ordinary mercury switches, which do not serve as circuit breakers and which are completely sealed in glass tubes, cannot be used for the present purpose.

Another peculiar consideration which has first been clearly recognized by applicant is that for minimum contact resistance it is necessary for mercury to cling to the electrode, instead of being drawn away by its own surface tension. The only metals which readily or dependably cause the mercury to cling to them are those metals which will amalgamate with mercury and hence be adversely afiected by it, particularly gold, silver and copper.

The first part of the present invention may be saidto be in discovering the facts heretofore stated. The facts, however, left a problem to be solved which was to reconcile the apparently conflicting requirements of a metal which would amalgamate with mercury (and hence have zero contact resistance even under adverse conditions and a metal which would satisfactorily withstand the eifect of mercury. There were of course the various other requirements to be met at the same time, which have already been mentioned.

In general, applicant has solved the problem by combining a metal which is satisfactory from the standpoint of a dependably low contactresistance in mercury'with a metal which is able to withstand satisfactorily being submerged in hot mercury and limit any detrimental reaction between the contact metal and mercury. This combination'may'be purely physical as if a small bit of copper or platinum is welded to the tip of an electrode. The platinum tip is satisfactory except for its cost and the cost is not prohibitive in the case of the feed electrode l6 where a very small amount of platinum may .be used since there .is no destruction of this electrode due to arcing. The cost is high enough, however, so that some other contact metal is preferred. No other single metalis known to be thoroughly satisfactory, although any high-conductive, heat resisting, non-oxidizing and non-amalgamating metal, probably including other members of the platinum group, would be. A tip or spot of gold or Y silver would be completely dissolved away and any pure copper would contaminate the mercury to some extent. The contamination seems to be especially severe because of a catalytic action of the copper in promoting mercury oxidation. The preferred solutions of the problem are, therefore, in the nature of a double combinationthe combination of a base electrode with a good contact forming tip, and a combination in the tip of a good contact forming metal and some other substance which limits the reaction between it and mercury.

Having reached this stage in the invention, one would except to find such a combination of metals to be used as a tip of an electrode among alloys, but it so happens that iron and nickel, cobalt, tungsten and any other metals of reasonable cost which best withstand the attack of mercury are not miscible with any of the metals which amalgamate with mercury, in suilicient proportions to product a thoroughly satisfactory alloy of reasonable cost. Nevertheless, there are some alloys which, although not as resistant to mercury as would be desired, are better than pure copper and in fact comprise the preferred form of the invention for a tip or spot on the feed'electrode. These alloys are in general combinations of an amalgamating metal and one or more other ingredients which retard the efiect of the mercury on the amalgamating metal. The best of these that has yet been found is beryllium-copper, which is satisfactory if exposed on the feed electrode in such a small quantity that its contamination of the mercury is not objectionable. One proportion found satisfactory is 2 beryllium and the rest copper. As seen in Figs. 2 and .3 one or more small pieces 26 of the berylliumcopper are spot welded to the electrode l6 which is preferably formed of cold rolled steel. The

beryllium-copper may be quite thin, .015 inch for example. Another known alloy which has some possibilities is that known commercially as Everdur containing 96% copper, 3% silicon, and 1% manganese. The use of this is restricted in the same way as that of beryllium-copper, but it contaminates the mercury more rapidly and hence is less satisfactory. Any other alloy may be used which contains copper (or other amalgamating metal) in suflicient proportions to amalgamate, and a non-amalgamating material decreasing the effect of the mercury on the amalgamating metal. The substances added to. the copper may be in any proportions so long as they reduce the reaction between it and mercury or the adverse effects thereof and do not too greatly raise its resistance or impair its amalgamating properties. With slightly less satisfactory results, any single metal which amalgamates without dis solving such as copper or manganese could be used. Instead of using the beryllium-copper or the Everdur or other such alloy or metal in such small quantities the entire electrode could be made of one of these materials and coated with a protective substance such as nickel plating except for a small spot exposed to the mercury.

Inasmuch'as copper oxidizes quite readily when exposed to the air it would not have been supposed prior to applicant's invention thatit or any of its alloys would be a good electrode in a switch such as that illustrated in which the electrode as a whole is exposed to air. Applicant has found that is spite of this fact it is a good contact metal except for the reaction between itand mercury because of the fact that the mercury amalgamates with it and apparently protects it from oxidation. Even if the housing I2 is turned so as to drain the mercury from the control tube and feed tube, a mercury film nevertheless remains on the contact spot of copper or copper alloy due to the fact that it is amalgamated with it. This film of mercury seems to stay in place indefinitely due to its ready amalgamation with the copper. With an iron electrode the amalgamation (even if forced temporarily by a'special process) would not last. The iron would consequently eventually be exposed to the air and become oxidized.

Although the use ofa small spot of berylliumcopper on the feed electrode 'is at present the preferred form of the invention with respect to the feed electrode, it is not regarded as a satisfactory solution of the problem for the discharge electrode. The discharge electrode has a special requirement that its tip, though formed of a good contact metal, must be sufliciently large to. withstand the severe effects of arcing and explosive discharges. A spot of beryllium-copper small enough not to contaminate the mercury might be melted away by the arcing.

The really satisfactory solution of the problem for the discharge electrode is found in making the tip 3| of the electrodes of a third class of combination of metals. This is a combination which seems to be physical in structure but chemical in effect, namely an intimate mixture of extremely fine particles of two metals. Metallic combinations of this kind have been known before and in fact some of them have been recommended for resistance to arcing. Their suitability for mercury electrodes has not been known heretofore. Such metallic combinations are preferably formed by a process known as sintering in which the desired proportions of the two metals are pulver ized and thoroughly intermixed after which the mixed powders are pressed in a mold and baked in an inert gas at such a temperature that they melt together even though they are not capable of dissolving one another in the proportions present. Of course, they must not be heated to such a temperature or for such a length of time that the two metals will completely melt and separate from one another.

Of the two metals which should be combined by th s sintering process or some analogous r cess one should be a metal of high conductivity which amalgamates with mercury while the other one should be a metal of high conductivity which does not amalgamate with mercury. Of course, the conductivity need not be extremely high in both instances if the average conductivity is sufficiently high, The amalgamable metal may be copper, silver or gold, for example. The nonamalgamable metal may be iron, nickel or tungsten, for example. The proportions may vary over a wide range so long as the amalgamable metal is present in a sufficient proportion to insure a low contact resistance and the other metal in a proportion sufficient to protect the amalgamable metal from too great reaction with the mercury.

One mixture which has been found to be especially satisfactory is silver 40% and iron 60%. Once the silver on the surface of such an electrode has been amalgamated (an acid treatment being required) the contact resistance is substantially zero and the amalgamation and low resistance seem to be permanent. The dissolving of the silver is very slow and seems to be definitely limited. Moreover, the silver has no detrimental efi'ect on the mercury. Likewise, the electrode is able to withstand satisfactorily the immersion in mercury at high temperature, aside from the slight and harmless dissolution already mentioned. The conductivity of the electrode both as to electricity and as to heat is quite satisfactory. Its resistance to destruction by arcing is also satisfactory. Another advantage is that it may be electrically welded directly to an iron electrode base 32 as seen in Fig. 4.

Another mixture which has been found to be satisfactory is 25% silver and 75% tungsten. This is superior to the silver and iron mixture in two respects, being a little more resistant to deterioration due to arcing and amalgamating a little more easily initially. The silver and iron combination is preferred, however, because of the low cost of iron and because the tungsten and silver combination, of the percentage named at least, is not thoroughly dependable in retaining its amalgamation and consequently its zero contact resistance.

A third mixture which has been tried with some good-cresults is 40% silver and 60% nickel. This is inferior to the silver and tungsten as well as to the silver and iron because the contact resistance is not dependably low.

A fourth mixture which is satisfactory, at least in small quantities, is 22% copper and 78% tungsten. In general copper is less desirable than the other amalgamating substances because to the extent that it does dissolve it may have an objectionable contaminating eifect on the,

mercury. Furthermore, this particular mixture is dimcult to amalgamate, although once amalgamated it remains amalgamated and the contact resistance remains zero.

In all of these mixtures the amalgamating metal not only forms a good contact with the mercury itself but maintains a film of mercury over or in amalgamation with the other metal and hence apparently protects the other metal from oxidation and insures a good electrical contact throughout. It is desirable, therefore, that the amalgamating metal be present in a suficient proportion to maintain the mercury film in protecting relationship with the other metal which does not ordinarily amalgamate with mercury readily. Of course, even with a smaller proportion of the amalgamating metal, some of the benefit of the mixture may nevertheless be obtained. The word maintain" as used in this application means to maintain the film (or the amalgamation) even if the electrode is removed from the main body of mercury as by turning the circuit controller of Fig. 1 to the ofi position.

Figs. 4 and 5 illustrate in detail one form of discharge electrode I! having a tip 3! resistancewelded thereon which is formed of one of the mixtures above discussed, such as the silveriron mixture, which may be called a silver-iron alley or a silver-iron sintered alloy for convenience.

Fig. 6 shows a detail sectional view of a modifled form of tip. The silver-tungsten alloy does not weld readily to the iron base 3! of the elec trode ii. To overcome this difliculty the tip 3 I is pressed onto an iron face 33 during sintering, the iron face having an undercut anchoring dowel 36 formed thereon. The assembly including the tip 3i and the iron face 33 may then be them.

resistance-welded to the iron plate ll 1.. It may be added that both the feed and discharge electrodes are desirably welded at their upper ends to tlie lead in studs shown in dotted lines in Fig.

From the foregoing it is seen that satisfactory electrodes are provided for a mercury circuit breaker or the like which need not be thoroughly sealed from the air. The invention contemplates particularly both a very cheap form of electrode such as the discharge electrode it, which need not be capable of withstanding much arcing, and a slightly more expensive electrode ill, which is capable of withstanding arcing. Both of the electrodes are thoroughly dependable in maintaining indefinitely a substantially zero contact resistance with the mercury without objectionably contaminating the mercury as would a plain copper electrode.

' The disclosures of this application are illustrative and the invention is not to be limited by In fact, if modifications or improvements are not at once obvious, they may be devised in the course of time'to make additional use of the broad ideas taught and covered by this application. The claims are intended to point out novel features and not to limit the invention except as may be required by prior art.

I claim: J r

l. A device for forming part of an electrical circuitcomprising a container, mercury in said container, and an electrode for said mercury which is sometimes exposed to air and subjected to arcing, said electrode including a supporting and conducting portion consisting chiefly of iron and substantially unafiected by the mercury in use and a tip portion welded thereto and including a contact tip positioned to contact said mercury and comprising a sintered mixture of silver in'a sufiicient proportion to maintain mercury in amalgamation with said contact tip even when it is separated from the main body of mercury, whereby a substantially zero contact resistance is assured, and iron in a non-miscible proportion sufiicient to limit the dissolving of said silver by said mercury.

2. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury including a supporting and conducting portion substantially unafi'ected by the mercury in use and a contact tippositioned to contact said mercury and including a sintered mixture of silver in a suificient proportion to maintain mercury in amalgamation with said contact tip even when it is separated from the main body of mercury and iron in a sufiicient proportion to limit the dissolving of said silver by said mercury.

3. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury which is sometimes subjected to arcing, said electrode including a supporting and conducting portion the exposed portion of which consists chiefly of metal unafiected by the mercury in use and 'a tip portion welded thereto and including a contact tip positioned to contact 'said mercury and comprising a sintered mixture of silver, in a suflicient proportion to maintain mercury in amalgamation with said contact tip even when it is separated from the main body of mercury, and a metal not readily amalgamated, in a sufllcient proportion to limit the dissolving of said silver by said mercury.

4. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury including a Supporting and conducting portion substantially unaffected by the mercury in use and a contact tip positioned to contact said mercury and including a sintered mixture of silver, in a suflicient proportion to maintain mercury in amalgamation with said contact tip even when it is separated from the main body of mercury, and a metal not readily amalgamated, in a sufiicient proportion to limit the dissolving of said silver by said mercury.

5. A device for forming part of an electrical circuit comprising a container, mercury .in said container, and an electrode for said mercury including a supporting and conducting portion substantially unaifected by the mercury in use and a contact tip positioned to contact said mercury and including a sintered mixture of a metal readily amalgamating with mercury, said material being in a sufilcient proportion to maintain mercury in amalgamation with said contact tip even when it is separated from the main body of mercury, and a metal not readily'amalgamated, in a sufiicient proportion to limit the dissolving of said amalgamating metal by said mercury.

6. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury sometimes exposed to air and including a supporting and conducting portion substantially unaffected by the mercury in use and a contact tip positioned to contact said mercury and including a sintered mixture of a metal readily amalgamating with mercury, said material being in a sufficient proportion to maintain mercury in amalgamation with said contact tip even when it is separated from the main body of mercury, and a metal not readily amalgamated, in a sufficient proportion to limit the dissolving of said amalgamating metal by said mercury.

7. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury sometimes exposed to air and including a supporting and conducting portion substantially unaffected by the mercury in use and a contact tip positioned to contact said mercury and including a substantially uniform combination of a metal readily amalgamating with mercury, said material being in a suificient proportion to maintain mercury in amalgamation -with said contact tip even when it is separated from the main body of mercury, and a metal not readily amalgamated, in a suflicient proportion to limit the dissolving of said amalgamating metal by said mercury.

8. A device for forming part of an electrical circuit comprising a container mercury in said container, and an electrode for 'said mercury sometimes exposed to air and arcing and including a supporting and conducting portion substantially unafiected by the mercury in use and a contact tip positioned to contact said mercury and including a substantially uniform combination of a metal readily amalgamating with mercury, said material being in a sufilcient proportion to maintain mercury in amalgamation with said contact tip even when it is separated from the main body of mercury, and a metal not readily amalgamated in a sufficient proportion to limit the dissolving of said amalgamating metal by said mercury, said contact tip having low electrical resistance and a sufllciently high melting point and conductivity of heat to satisfactorily resist arcing.

9. A device for forming part of an electrical circuit comprising a container, mercury in said container, and a conductive electrode for said mercury sometimes exposed to air and which is formed at least in part of a metal which does not readily amalgamate with mercury and a sumcient amount of a metal which amalgamates with mercury to maintain a low resistance contact with the mercury.

10. A device for forming part of an electrical circuit comprising a container, mercury insaid container, and a conductive electrode for said mercury sometimes exposed to air and which includes a portion formed predominantly of two metals in substantial quantities, one of which readily amalgamates with the mercury and the other of which does not and which reduces the cfiects of the amalgamation of the first named metal.

11. A device for forming part of an electrical circuit comprising a container, mercury in said container, and a conductive electrode for said mercury which is formed at least in part of a sintered mixture of a sufficient proportion of a metal which readily amalgamates with mercury to maintain amalgamation with mercury even when removed from the main body of mercury and one which does not readily amalgamate with mercury.

12. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury sometimes exposed to air and which is formed at least in part of a combination of a metal which amalgamates readily with mercury and a I substance which limits or retards the amalgamation of said metal, said combination being further characterized by maintaining amalgamation with mercury even when removed from the main body of mercury and by satisfactory electrical conductivity.

13. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury sometimes exposed to air and which includes a supporting and conducting portion which is formed of conductive metal and which does not amalgamate with mercury in use but which oxidizes and a conductive contact portion which is carried by the first named portion and does not oxidize when exposed to air in use and maintains a low resistance contact with the mercury.

14. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury sometimes exposed to air and which includes a supporting and conducting portion which is formed of conductive metal and which does not amalgamate with mercury in use but which oxidizes and a conductive contact portion which is carried by the first named portion and maintains a low resistance contact with the mercury because of amalgamation, said contact portion being capable of maintaining its amalgamation with the mercury when removed from the main body of mercury and exposed to air.

15. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury sometimes exposed to air and which includes a supporting and conducting portion which does not amalgamate with mercury in use but which oxidizes and a conductive contact portion which is carried by the first named portion and main= tains a low resistance contact with the mercury because of amalgamation, said contact portion including a metal which oxidizes if exposed to. air but amalgamates with mercury so readily as to maintain suflicient mercury thereon, when removed from the main body of mercury, to protect .it from oxidation.

3.6;A circuit controller container, mercury in saidcontainer, a small bored member through which the mercury must flow, and an electrode for said mercury sometimes exposed to air and which includes a supporting and conducting portion which does not amalgamate with mer-' cury in use but which oxidizes and a conductive contact portion which is carried by the first named portion and'maintains a low resistance contact with the mercury, said contact portion being formed of copper in a predominant proportion but with only a small surface thereof exposed, another material not afiected by the mercury, in a proportion to prevent said copper from objectionably contaminating the mercury, and a protective amount of mercury amalgamated with CERTIFICATE Patent Not 2,13%986,

STANLEY S GREEN with the mercury, said contact portion being formed of an amalgamable metal of limited solubility in a predominant proportion but with a small surface thereof exposed, and mercury amalgamated thereon.

18. A device for forming part of an electrical circuit comprising a container, mercury in said container, and an electrode for said mercury sometimes exposed to air and which includes a supporting and conducting portion which does not amalgamate with mercury in use but oxidizes and a conductive contact portion which is carried by the first named portion and maintains a low resistance contact with the mercury, said contact portion being formed of beryllium-copper having mercury amalgamated with its surface portion.

19. An electrode for mercury including a body portion substantially unaffected by mercury and a contact portion comprising a substantially uniform combination of suflicient proportion of a metal amaigamating with mercury to maintain amalgamation with mercury even when re- 'moved from the main body of mercury and a substance for reducing the adverse eflects of reaction between said substance and the mercury.

20. An electrode for mercury, at least part of which is formed of an amalgamable metal of limited solubility in a predominant proportion but coated except in a small exposed spot with a stance substantially unaffected by the mercury,

said small exposed spot being positioned to con-' tact the mercury and become amalgamated OF CORRECTIONO October-25, 19 8-.

It is hereby certified that error appears in the printed specification of the'above numbered patent requiring correction as follows: Page 6, second column, line 51, claim 20, for "stance? read substance; and that the said.

Letters Patent should be read with this correction therein that/the same may conform to the record of the case in the Patent Offices Signed and sealed this th day of December, A, o. 195

"(S.eal)

Henry Van Arsdale Acting Commissioner of Pate'nt's. 

